A short-cut from 1-acetyl adamantane to 2-(1-adamantyl)pyrroles

Article abstract of DOI:10.1016/j.tetlet.2008.05.023

The oxime of 1-acetyl adamantane 2 is added to acetylene (KOH/DMSO, 70 °C, initial acetylene pressure 13 atm, 30 min) to afford the corresponding O-vinyl oxime 5 in 80% yield. The latter upon heating (DMSO, 120 °C, 1 h) gives 2-(1-adamantyl)pyrrole 3, 1-acetyl adamantane 1, and adamantane (6:3:1 mass ratio), the yield of the pyrrole 3 being 83% (based on 1-acetyl adamantane 1 consumed). Under harsher conditions (NaOH/DMSO, 130 °C, atmospheric pressure of acetylene, 4 h) oxime 2 reacts with acetylene to furnish pyrrole 3, 1-acetyl adamantane 1, 1-vinyl adamantane 9, and adamantane (6:7:3:1 mass ratio), with the isolated yield of pyrrole 3 reaching 34%. Under pressure (NaOH/DMSO, 120 °C, initial acetylene pressure 14 atm, 1 h) the same reaction leads to 2-(1-adamantyl)-1-vinylpyrrole 4 and ketone 1 in 48% (based on consumed ketone 1) and 24% yields, respectively. The pyrrole 4 is easily deprotected to the corresponding 1H-pyrrole 3 in 77% yield by treatment (aqueous MeCN) with Hg(OAc)₂ and NaBH₄.

Full text of DOI:10.1016/j.tetlet.2008.05.023

Tetrahedron Letters 49 (2008) 4362–4365
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Tetrahedron Letters
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A short-cut from 1-acetyl adamantane to 2-(1-adamantyl)pyrroles
a
a
a
Boris A. Trofimov a, , Elena Yu. Schmidt , Nadezhda V. Zorina , Elena Yu. Senotrusova ,
*
Nadezhda I. Protsuk a, Igor A. Ushakov a, Al’bina I. Mikhaleva a, Rachel Méallet-Renault b, Gilles Clavier b
a A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 1 Favorsky Str., Irkutsk 664033, Russian Federation
b PPSM, ENS Cachan, CNRS, UniverSud, 61 av President Wilson, F-94230 Cachan, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The oxime of 1-acetyl adamantane 2 is added to acetylene (KOH/DMSO, 70 °C, initial acetylene pressure
13 atm, 30 min) to afford the corresponding O-vinyl oxime 5 in 80% yield. The latter upon heating (DMSO,
120 °C, 1 h) gives 2-(1-adamantyl)pyrrole 3, 1-acetyl adamantane 1, and adamantane (6:3:1 mass ratio),
the yield of the pyrrole 3 being 83% (based on 1-acetyl adamantane 1 consumed). Under harsher condi-
tions (NaOH/DMSO, 130 °C, atmospheric pressure of acetylene, 4 h) oxime 2 reacts with acetylene to fur-
nish pyrrole 3, 1-acetyl adamantane 1, 1-vinyl adamantane 9, and adamantane (6:7:3:1 mass ratio), with
the isolated yield of pyrrole 3 reaching 34%. Under pressure (NaOH/DMSO, 120 °C, initial acetylene pres-
sure 14 atm, 1 h) the same reaction leads to 2-(1-adamantyl)-1-vinylpyrrole 4 and ketone 1 in 48% (based
on consumed ketone 1) and 24% yields, respectively. The pyrrole 4 is easily deprotected to the corre-
sponding 1H-pyrrole 3 in 77% yield by treatment (aqueous MeCN) with Hg(OAc)2 and NaBH4.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 2 April 2008
Revised 30 April 2008
Accepted 7 May 2008
Available online 10 May 2008
Keywords:
Pyrrole
Adamantane
Oxime
Acetylene
O-Vinyloxime
2-(1-Adamantyl)pyrrole
The chemistry of adamantane continues to attract attention
due to the high biological activity of its derivatives. Their hydro-
phobicity and lypophilicity favor transport of adamantane com-
pounds across biological membranes.1 Combination of the
adamantane structure with heterocyclic compounds modifies
their biological activity, often enhancing the effect or imparting
a new kind of activity.2 For example, acylguanidines with an ada-
mantyl–pyrrolyl moiety were shown recently to be b-secretase
inhibitors related to Alzheimer’s disease.3 Dipyrromethanes with
an adamantane moiety at the bridge exhibit properties of anion
receptors.4 Adamantane–pyrrole ensembles are promising targets
in adamantane and pyrrole chemistry as well as for drug design.
Pyrroles with bulky substituents such as adamantyl are employed
for the construction of new high-performance BODIPY fluoro-
phores with improved fluorescent properties due to prevention of
p-stacking.5 However, until now, adamantane–pyrrole ensembles
remain scarcely known. 2-Adamantyl pyrrole was reported (but
O
NOH
Me
NH OH
HCl
2
80 oC, 2 h
Me
2
1
97%
HC CH
2
+
N
N
H
4
3
Scheme 1.
of ZnCl2 (2–5 days, 44% yield). The poorly characterized (only
mp and nitrogen elemental analysis data) 2,5-di(1-adaman-
tyl)pyrrole was synthesized from 1,4-di(adamantyl)butane-1,4-
dione and ammonia in 33% total yield (over 4 steps starting from
1-acetyl adamantane).7 Thus, the synthesis of adamantyl pyrroles
still remains a challenge for the development of adamantane–pyr-
role chemistry.
In this Letter, we report the first example of an easy, short trans-
formation of 1-acetyl adamantane 1 (via the oxime 2) to 2-(1-ada-
mantyl)pyrrole 3 and its 1-vinyl derivative 4 through the reaction
of the oxime 2 with acetylene in the presence of different super-
base catalytic systems (MOH/DMSO, M = Na or K) using a modifica-
tion of the Trofimov reaction (Scheme 1).8
not characterized) using
a multi-step protocol starting from
tributyl(vinyl)stannane via the intermediate lithiated dibenzyl-
cyclopropylamine, which further reacted with nitriles.6 (2-Ada-
mantyl-5-phenylpyrrolyl-1-yl)acetic acid and its guanidine
derivative were prepared from 1-adamantyl-4-phenylbutane-
1,4-dione and glycine in 57% and 22% yields (final step), respec-
tively, the above diketone being prepared by coupling of 1-ada-
mantylbromomethyl ketone and acetophenone in the presence
* Corresponding author. Tel.: +7 395251 19 26; fax: +7 395241 93 46.
E-mail address: boris_trofimov@irioch.irk.ru (B. A. Trofimov).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.05.023

B. A. Trofimov et al. / Tetrahedron Letters 49 (2008) 4362–4365
4363
Me
HC CH, KOH/DMSO
70 oC, 30 min
DMSO
5
2
+
+
1
N
N
O
5
H
3
80%
Scheme 4.
Scheme 2.
R
R
CH3
R
[1,3]
H
[3,3]
- H2O
R
R
HN
N
N
HN
OH
N
O
O
O
H
7
8
6
R = adamantyl
Scheme 3.
HC CH, NaOH/DMSO
2
+
1
+
+
N
H
9
3
Scheme 5.
Initially, we found that the oxime 2 (prepared from 1-acetyl
adamantane 1 in 97% yield)9 readily reacts with acetylene under
pressure in the KOH/DMSO system (70 °C, initial acetylene pressure
13 atm, 30 min) to form exclusively the corresponding O-vinyl
oxime 510 in 80% isolated yield (Scheme 2).
Under pressure in the same catalytic system (initial acetylene
pressure 14 atm, 120 °C, 1 h), 2-(1-adamantyl)-1-vinylpyrrole 415
and 1-acetyl adamantane 1 were formed in 48% and 24% yields
(the former yield is based on the starting ketone 1 consumed)
(Scheme 6).
It is commonly recognized5,11 that the key step of pyrrole syn-
thesis from an O-vinyl ketoxime is the [3,3]-rearrangement of its
O-vinylhydroxylamine tautomer 6 to an iminoaldehyde 7, which
further ring closes to a hydroxypyrroline 8, and undergoes dehy-
dration and finally aromatization to the pyrrole (Scheme 3).
Upon heating O-vinyl oxime 5 in DMSO (120 °C, 1 h), it rear-
ranged to 2-(1-adamantyl)pyrrole 3, other products being 1-acetyl
adamantane 1 and adamantane (their ratio in the crude product
was 6:3:1, as determined by GLC),13 (Scheme 4). The calculated
yield (based on the product ratio) of the pyrrole 3 is 57%, while
the isolated yield was 30% because significant amounts of the pyr-
role 3 are distributed between other eluted fractions during the
chromatographic (column) separation. In fact, since the recovered
1-acetyl adamantane 1 can be returned to the synthesis (Scheme
1), the actual yield of the pyrrole 3 calculated from the mass of
1-acetyl adamantane 1 consumed is higher (in this case, 83% based
on the GLC composition of the crude product).
1-Vinyl pyrrole 4 (due to its reactive N-vinyl group8a,16,17) rep-
resents a prospective monomer and promising building block for
the design of diverse polymeric and monomeric compounds con-
taining the adamantylpyrrole structural unit. Besides, the pyrrole
4 is in fact protected NH-pyrrole 3, which augments its synthetic
potential further. Indeed, the vinyl group can be readily removed
by treatment of pyrrole 4 with mercury acetate and reaction of
the intermediate with sodium borohydride (50 °C, 40 min). The
yield of the deprotected pyrrole 318 was 77% (Scheme 7).
This modification of the reaction of ketoximes with acetylene
exhibits remarkable peculiarities, namely the deoximation forming
1-vinyl adamantane 9 and adamantane.
The deoximation occurs both during O-vinyl oxime 5 rearrange-
ment and the direct synthesis of pyrroles 3 and 4 from oxime 2, the
latter proceeding via the intermediate O-vinyl oxime 5. The rear-
rangement 5?1 may be explained by the isomerization of O-vinyl
oxime 5 to N-vinyl nitrone 5a, which is further transformed to
In the NaOH/DMSO system at one atmospheric pressure of acet-
ylene and a higher temperature (130 °C, 4 h), pyrrole 3 was synthe-
sized directly from the oxime 2 in a one-pot procedure, thus
avoiding isolation of the intermediate O-vinyl oxime 5. In this case,
together with the major products, pyrrole 3 and 1-acetyl adaman-
tane 1, 1-vinyl adamantane 9 and adamantane were also formed,
the mass ratio of the products in the crude being 6:7:3:1 (GLC).
From this mixture pyrrole 3, 1-acetyl adamantane 1, and adaman-
tane were isolated by column chromatography in 34%, 12% and 3%
yields (Scheme 5). The yield of the pyrrole 3 was calculated based
on the mass of 1-acetyl adamantane 1 consumed. 1-Vinyl adaman-
tane 9 was identified by 1H NMR14 and GCMS.
HC CH, NaOH/DMSO
2
1
+
N
4
Scheme 6.
NaBH4
Hg(AcO)2
4
3
N
HgOAc
AcO
The main hazards in handling acetylene at or above atmospheric pressure are
comprehensively highlighted in a basic monograph.12
Scheme 7.

4364
B. A. Trofimov et al. / Tetrahedron Letters 49 (2008) 4362–4365
Me
Me
Me
Me
N
+
O
N+
10
N
O
N
O
1
5
5b
5a
-
O
MeCO2M + NH3
MeCN
10
Scheme 8.
Me
Me
N+
N
polymer
+
O
11
5a
-
O
+
HC CH
9
Scheme 9.
8. (a) Trofimov, B. A. In Adv. Heterocycl. Chem; Academic Press: San Diego,
1990; Vol. 51. pp 177–301; (b) Trofimov, B. A. The Synthesis, Reactivity,
and Physical Properties of Substituted Pyrroles; Wiley: New York, 1992. pp
131–298; (c) Mikhaleva, A. I.; Schmidt, E. Yu. In Selected methods for
synthesis and modification of heterocycles; IBS Press: Moscow, 2002; Vol. 1.
pp 334–352.
ketone 1 as shown in Scheme 8. Vinyl nitrene 10, released by the
decomposition of the intermediate oxazirane 5b, isomerizes proto-
tropically to acetonitrile, which is oxidized under the action of
alkaline metal hydroxides to sodium or potassium acetates
(Scheme 8).
The formation of 1-vinyl adamantane 9 is rationalized by an
alternative decomposition of nitrone 5a to deliver carbene 11
and nitrosoethene (Scheme 9). The carbene 11 rearranges to 1-vin-
yl adamantane 9.
Also noteworthy is the fact that the studied reaction allows O-
vinyl oximes 5 of acyl adamantanes, novel highly reactive deriva-
tives of adamantane, to be synthesized readily in high yield
(Scheme 2).
9. A mixture of 1 (1.00 g, 5.6 mmol), H2NOHÁHCl (2.90 g, 7.0 mmol) and pyridine
(15 mL) was heated (80 °C) for 2 h and then poured into water (80 mL). The
crystalline precipitate was filtered off, washed with water and dried in vacuo
to afford 1.05 g (yield 97%) of 2 as a white powder, mp 182–184 °C. 1H NMR
(400.13 MHz, CDCl3): d 8.82 (s, 1H, OH), 2.01 (m, 3H, H3, H5, H7), 1.82 (s, 3H,
Me), 1.75 (m, 6H, H4, H6, H10), 1.67 (m, 6H, H2, H8, H9). 13C NMR
(101.61 MHz, CDCl3): d 164.6 (C@N), 39.3 (C2, C8, C9), 38.3 (C1), 36.8 (C4,
C6, C10), 28.1 (C3, C5, C7), 9.2 (Me). IR (KBr) mmax: 3227 (OH), 1659 (C@N),
1446, 1359, 1342, 1270, 1010, 984, 936, 859, 771, 732, 665, 554, 459 cmÀ1
.
Anal. Calcd for C12H19NO (193.29): C, 74.57; H, 9.91; N, 7.25. Found: C, 74.78;
H, 9.98; N, 7.25.
10. A mixture of 2 (2.00 g, 10.3 mmol) and KOHÁ0.5H2O (0.84 g, 12.9 mmol) was
dissolved under heating (70 °C) in DMSO (50 mL). The solution of potassium
oximate thus obtained was placed into a 0.25 L steel rotating autoclave. Then
acetylene gas was transferred to the autoclave to remove air and the autoclave
was charged with acetylene again from a cylinder at room temperature (initial
pressure 13 atm). The autoclave was heated upon rotating (70 °C) for 30 min.
The reaction mixture, after being cooled to room temperature, was extracted
with pentane (10 mL Â 7). The pentane extracts were washed with cold water
(10 mL Â 3) to remove dissolved DMSO. The mixture was dried over K2CO3
overnight and the pentane was removed to yield a residue (1.93 g). After
column chromatography (basic Al2O3, hexane–ether 3:1) pure 5 was obtained
(1.81 g, 80%) as white crystals (mp 113–114 °C). 1H NMR (400.13 MHz, CDCl3):
Thus, a short-cut from 1-acetyl adamantane to 2-(1-adaman-
tyl)pyrrole and 2-(1-adamantyl)-1-vinylpyrrole via the isolable
intermediate O-vinyl oxime of 1-acetyl adamantane through the
reaction of the oxime of 1-acetyl adamantane with acetylene in
MOH/DMSO superbase systems has been realized. The combina-
tion of adamantane and pyrrole chemistry may lead to target com-
pounds such as drugs, fluorophores including BODIPY and other
advanced optoelectronic materials.
3
3
3
d 6.88 (dd, 1H, JBX = 14.2 Hz, JAX = 6.8 Hz, HX), 4.55 (dd, 1H, JBX = 14.2 Hz,
2JAB = 1.4 Hz, HB), 4.04 (dd, 1H, 3JAX = 6.8 Hz, 2JAB = 1.4 Hz, HA), 2.01 (m, 3H, H3,
H5, H7), 1.82 (s, 3H, Me), 1.77 (m, 6H, H4, H6, H10), 1.72 (m, 6H, H2, H8, H9).
13C NMR (101.61 MHz, CDCl3): d 166.6 (C=N), 152.8 (Ca), 87.0 (Cb), 39.3 (C2, C8,
Acknowledgments
The authors are grateful to the Russian Foundation for Basic Re-
search (Grant 07-03-92162-PICS_a) and the French Centre National
de la Recherché Scientifique (PICS 3922) for financial support.
C9), 38.3 (C1), 36.6 (C4, C6, C10), 28.0 (C3, C5, C7), 10.2 (Me). IR (KBr) mmax
:
2903, 2849, 1640, 1614, 1449, 1376, 1344, 1275, 1253, 1168, 1006, 985, 953,
888, 863, 831, 649. Anal. Calcd for C14H21NO (219.33): C, 76.67; H, 9.65; N,
6.39. Found: C, 77.00; H, 9.71; N, 6.69.
11. Schmidt, E. Yu.; Zorina, N. V.; Zaitsev, A. B.; Mikhaleva, A. I.; Vasil’tsov, A. M.;
Audebert, P.; Clavier, G.; Meallet-Renault, R.; Pansu, R. B. Tetrahedron Lett.
2004, 45, 5489–5491.
12. Miller, S. A. In Acetylene. Its Properties, Manufacture, and Uses; Ernest Benn
Limited: London, 1965; Vol. 1, p 506.
References and notes
1. Litvinov, V. P. Khim. Geterotsikl. Soed. 2002, 1, 12–39; Litvinov, V. P. Chem.
Heterocycl. Compd. 2002, 38, 9–34.
2. Shvekheimer, M.-G. A. Russ. Chem. Rev. 1996, 65, 603–647.
3. Cole, D. C.; Manas, E. S.; Stock, J. R.; Condon, J. S.; Jennings, L. D.; Aulabaugh, A.;
Chopra, R.; Cowling, R.; Ellingboe, J. W.; Fan, K. Y.; Harrison, B. L.; Hu, Y.;
Jacobsen, S.; Jin, G.; Lin, L.; Lovering, F. E.; Malamas, M. S.; Stahl, M. L.; Strand, J.;
Sukhdeo, M. N.; Svenson, K.; Turner, M. J.; Wagner, E.; Wu, J.; Zhou, P.; Bard, J. J.
Med. Chem. 2006, 49, 6158–6161.
4. Renic, M.; Basaric, N.; Mlinaric-Majerski, K. Tetrahedron Lett. 2007, 48, 7873–
7877.
5. Zaitsev, A. B.; Méallet-Renault, R.; Schmidt, E. Yu.; Mikhaleva, A. I.; Badré, S.;
Dumas, C.; Vasil’tsov, A. M.; Zorina, N. V.; Pansu, R. B. Tetrahedron 2005, 61,
2683–2688.
13. A solution of 5 (1.35 g, 6.2 mmol) in DMSO (20 mL) was heated at 120 °C for
1 h. The mixture was diluted with water (50 mL), extracted with diethyl ether
(10 mL Â 5), and the combined organics were washed with water (5 mL Â 3)
and dried over K2CO3 overnight. Evaporation of the solvent gave 1.17 g of crude
product with the 3:1:adamantane ratio being 6:3:1 (GLC), corresponding to a
57% yield of 3. Column chromatography (basic Al2O3, hexane–diethyl
ether = 10:1) afforded 0.37 g (30% yield) of 3, 0.30 g (27% yield) of 1, and
0.09 g (11% yield) of adamantane.
3
3
14. Compound 9: 1H NMR (400.13 MHz, CDCl3): d 5.72 (dd, 1H, JBX 17.5 Hz, JAX
3
3
10.8 Hz, HX), 4.86 (d, 1H, JBX 17.5 Hz, HB), 4.84 (d, 1H, JAX 10.8 Hz, HA), 2.00
(m, 3H, H3, H5, H7), 1.70 (m, 6H, H4, H6, H10), 1.60 (m, 6H, H2, H8, H9). GCMS
(ES) m/z 162.
6. Tanguy, C.; Bertus, Ph.; Szymoniak, J.; Larionov, O. V.; de Meijere, A. Synlett
2006, 2339–2341.
7. Stetter, H.; Rauscher, E. Chem. Ber. 1960, 93, 2054–2057.
15. A mixture of 2 (1.00 g, 5.2 mmol) and NaOH (0.21 g, 5.2 mmol) was dissolved
under heating (80–90 °C) in DMSO (50 mL). The solution of sodium oximate
thus obtained was placed into a 0.25 L steel rotating autoclave. Then acetylene

B. A. Trofimov et al. / Tetrahedron Letters 49 (2008) 4362–4365
4365
gas was transferred to the autoclave to remove air and the autoclave was
charged with acetylene again from a cylinder at room temperature (initial
pressure 14 atm). The autoclave was heated upon rotating (120 °C) for 1 h. The
reaction mixture, after cooling to room temperature, was extracted with
diethyl ether (15 mL Â 5). The ether extracts were washed with cold water
(15 mL Â 3) to remove dissolved DMSO and dried over K2CO3 overnight.
Column chromatography (basic Al2O3, hexane) of the residue (1.51 g) after
evaporation of the diethyl ether gave 0.44 g (yield 48% based on 1-acetyl
adamantane 1 consumed) of 4 as white crystals (mp 106–108 °C) and 0.22 g of
1 (yield 24%). Compound 4: 1H NMR (400.13 MHz, CDCl3): d 7.33 (dd, 1H,
3JBX = 15.8 Hz, 3JAX = 8.6 Hz, HX), 6.87 (m, 1H, H5pyr), 6.08 (m, 1H, H3pyr), 5.92
(m, 1H, H4pyr), 5.05 (d, 1H, JBX = 15.8 Hz, HB), 4.69 (d, 1H, JAX = 8.6 Hz, HA),
2.04 (m, 3H, H3, H5, H7), 2.00 (m, 6H, H4, H6, H10), 1.74 (m, 6H, H2, H8, H9).
13C NMR (101.61 MHz, CDCl3): d 142.0 (C2pyr), 134.0 (Ca), 119.0 (C5pyr), 108.3
(C4pyr), 106.4 (C3-pyr), 99.8 (Cb), 42.1 (C2, C8, C9), 36.6 (C4, C6, C10), 34.4
(C1), 28.7 (C3, C5, C7). IR (KBr) mmax: 3445, 2904, 2848, 1635, 1476, 1449, 1420,
1281, 1101, 862, 711. Anal. Calcd for C16H21N (227.35): C, 84.53; H, 9.31; N,
6.16. Found: C, 84.58; H, 9.12; N, 6.19.
17. Schmidt, E. Yu.; Senotrusova, E. Yu.; Ushakov, I. A.; Protsuk, N. I.; Mikhaleva, A.
I.; Trofimov, B. A. Zh. Org. Khim. 2007, 43, 1502–1508; Schmidt, E. Yu.;
Senotrusova, E. Yu.; Ushakov, I. A.; Protsuk, N. I.; Mikhaleva, A. I.; Orofimov, B.
A. Russ. J. Org. Chem. 2007, 43, 1495–1501.
18. Procedure for the synthesis of 3 by deprotection of 4. Mercury acetate (2.12 g,
6.6 mmol) in 25 mL of 10% aqueous acetonitrile was added to
4 (0.50 g,
2.2 mmol) in 25 mL of acetonitrile under stirring. The reaction mixture was
stirred for 40 min at 50 °C, then NaBH4 (0.38 g, 8.2 mmol) was added in small
portions. After gas evolution was complete, the residue was filtered off. The
filtrate was diluted with brine (50 mL), extracted with diethyl ether
(15 mL Â 3), and the combined ether extracts were dried over E2CI3
overnight. The ether was removed to give 0.34 g (yield 77%) of 3 as white
crystals (mp 100–102 °C). 1H NMR (400.13 MHz, CDCl3): d 8.01 (br s, 1H, NH),
6.66 (m, 1H, H5pyr), 6.13 (m, 1H, H4pyr), 5.91 (m, 1H, H3pyr), 2.04 (m, 3H, H3,
H5, H7), 1.88 (m, 6H, H4, H6, H10), 1.74 (m, 6H, H2, H8, H9). 13C NMR
(101.61 MHz, CDCl3): d 135.7 (C2pyr), 115.7 (C5pyr), 107.9 (C3pyr), 101.8
(C4pyr), 43.0 (C2, C8, C9), 36.9 (C4, C6, C10), 36.8 (C1), 28.7 (C3, C5, C7). IR
(KBr) mmax: 3387, 2905, 2845, 1563, 1470, 1450, 1419, 1365, 1341, 1317, 1125,
1001, 1028, 782, 724, 712, 570. Anal. Calcd for C14H19N (201.31): C, 83.53; H,
9.51; N, 6.96. Found: C, 83.68; H, 9.23; N, 7.11.
3
3
16. Vasil’tsov, A. M.; Ivanov, A. V.; Ushakov, I. A.; Mikhaleva, A. I.; Trofimov, B. A.
Synthesis 2007, 452–456.